The invention relates to a process for realizing a leakage-free switching double seat valve adapted for cleaning seat surfaces according to the preamable of the main claim.
European Pat. No. 00 44 517 discloses a method and apparatus permitting the simultaneous cleaning of both seat surfaces of a double seat valve while product is present on at least one side of the valve.
In some instances, in particular when using double seat valves in the food processing industry, it is an advantage when switching of the valves can be accomplished without leakage. The term switching leakage is understood as that amount of fluid which in a switching operation leaks from a valve casing part via the respective exposed seat surface into the leakage cavity. If a double seat valve is capable of leakage-free switching owing to its basic structure, such switching leakage will occur both during the open and closing movements of the valve.
Of the various types of double seat valves disclosed in FIGS. 1 to 5a of European Pat. No. 00 44 517, only FIGS. 1 to 3a show types of valves that can provide leakage-free switching. Moreover, none of these five basic types permits a separate cleaning of the seat surface of the piston closing element on which possibly the product acts through the leakage cavity by means of cleansing agent supplied from outside the double seat valve. Such a cleaning method, however, is actually necessary whenever product is in contact with the other valve casing part, which is closed by the seat disk, or cleansing agent cannot otherwise be made available.
On the basis of the above-indicated state of the art, it is an object of the instant invention to provide leakage-free switching and the simultaneous cleaning of the seat surfaces of both closing elements, as well as the separate cleaning of the seat surface of the piston-like closing element while in contact with the product.
The method according to the invention for the first time ensures that all of the double seat valves of the types indicated above will be able to switch without leakage.
In addition, for the types of valves known to switch without leakage prior to the present invention, the invention provides a particularly safe and efficient coupling of the two closing elements since said coupling is no longer solely determined by the opening or closing movement of the double seat valve, but rather, is precisely controlled and the amount of force of the two closing elements results, as is known, from the spring tension with which the latter are braced relative to each other. The spring tension is greatest in the decoupled position of the closing elements; it decreases by an amount corresponding to the relative distance travelled during the lift and then remains practically unchanged during the entire period in which the double seat valve is in the open position.
In a preferred embodiment, by supplying the cleansing agent from outside the double seat valve through the leakage cavity, separate cleaning of the seat surface of the piston-like closing element which may be in contact with the product is provided, since according to the invention it is movable individually from its resting position toward the valve casing part which may be carrying the product.
Another aspect of the invention provides that the cleansing agent supplied from outside the double seat valve, upon exceeding a selectively adjustable pressure, initiates the switching sequence which then proceeds in a manner determined by the design of the valve for cleaning the seat of the piston-like closing element. In this manner the external control action required for cleaning the seat surfaces of the double seat valve is reduced to supplying a cleansing agent with the appropriate pressure when cleaning is required.
In another preferred embodiment of the invention, the external control action necessary for opening and closing the double seat valve is reduced in that the switching sequence in accordance therewith proceeds in a manner determined by the design of the valve after being initiated from outside the double seat valve. Since the blocking device and the space between the drive pistons therein are controlled always in the same manner, at most out of phase, a maximum of three control signals are required in a switching operation of the double seat valves (opening movement into open position, closing movement into closed position) according to the switching sequence of the invention. Thus, only one external control signal (open valve, close valve) is needed; the two others are generated internally.
In accordance with a further embodiment of the invention, cleaning of the seat surfaces can be intensified, particularly in the seat area of the closing element that may be in contact with the product, by repeating the partial lift movements several times.
In order to secure the seat disk against being forced out of its closing position by accidently applied counter pressure or impacts, additional force is provided selectively by a further aspect of the invention to press the aforesaid seat disk against its seat surface.
A further advantageous aspect of the invention provides a closing element such that the pressure forces exerted on the closing element by fluid in the valve casings are largely compensated. Such a measure renders the provision of additional force for the arresting movement of the closing element superfluous.
European Pat. No. 00 44 517 is addressed to the objective of the particular invention stressed therein, i.e., to permit the simultaneous cleansing of both seat surfaces of a double seat valve while product is present on at least one side of the valve, for the five basic types of valves illustrated in FIGS. 1 to 5a. However, a detailed description is provided only for the type of double seat valve that is shown in FIG. 4. The present invention not only addresses the particular objects listed above but incidentally concretely illustrates examples of apparatus suitable for providing simultaneous cleaning of the seat surfaces of both closing elements for other types of valves in accordance with that invention, in addition to the objects of the present invention listed above.
By the proposed apparatus for performing the method according to the invention it is possible for the first time to realize all of the functions relevant in the operation of double seat valves of the type characterized in the introduction in a concrete solution "as a harmonious whole", namely
the leakage-free switching,
the simultaneous cleaning of the seat surfaces of both closing elements,
the separate cleaning of the seat surface of the structurally slide-like closing element possibly acted upon by the product by means of the supply of cleansing agent from the leakage cavity and
the additional pressing of the closing element structurally formed as seat disk to its seat surface by means of an additional force
or alternatively to the last-named function
the compensation of the pressure forces exerted by the fluid in the pipes on the closing elements.
In advantageous modification of the apparatus according to the invention, the drive piston of the closing element which during the opening movement of the double seat valve is shifted into open position by the other closing element, is sealingly slidable on its valve stem during the opening movement of the double seat valve, while in the opposite direction of shifting it will engage form-closed on said valve stem via a collar. By this unilaterally effective separation between drive piston and associated valve stem there is achieved a simplification of the control. While, without said separation in the open position of the double seat valve, there must be controlled simultaneously two spaces (space between the pistons and a further space), the control in case of the separation of the drive piston from its valve stem, is reduced to the pressure load on the space between the pistons.
A further advantageous aspect of the apparatus according to the invention overcomes the partial lift limitation of drive pistons in apparatus where the partial lift is limited by a stop member located in the space between the drive pistons. The stop in the apparatus according to the present invention is disposed on a casing of the actuating device. This is feasible for configurations of the closing elements in which the piston-like closing element shifts the other closing element into an open position.
According to another advantageous aspect of the apparatus, the space between the drive pistons communicates via a passage therein or through the annular gap around the valve stem with the surroundings of the double seat valve. In this way the pressure agent is supplied, in a simple manner that is independent of valve movements, to the space between the drive pistons which changes in both its size and its position during the switching movement of the double seat valve.